Wells are generally drilled into the ground or ocean bed to recover natural deposits of oil and gas, as well as other desirable materials that are trapped in geological formations in the earth's crust. A well is drilled into the ground and directed to the targeted geological location from a drilling rig or platform at the surface of the earth. The well may be formed using a drill bit attached to the lower end of a drill string formed with a plurality of drill pipe (or drill pipe collars). Drilling fluid, or mud, is typically pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the drill bit, and carries drill cuttings back to the surface in the annulus between the drill string and a wellbore wall.
For successful oil and gas exploration, it is advantageous to have information about the subterranean formations that are penetrated by a wellbore. For example, one aspect of standard formation testing relates to the measurements of the formation pressure and formation permeability. Another aspect of standard formation testing relates to the extraction of formation fluid for fluid characterization, in situ or in surface laboratories. These measurements are useful to predicting the production capacity and production lifetime of a subterranean formation.
Well logging tools are devices configured to move through a wellbore drilled through subterranean formations. The well logging tools include one or more devices that measure various properties of the subterranean formations and/or perform certain mechanical acts on the formations, such as drilling or percussively obtaining samples of the subterranean formations, and withdrawing samples of connate fluid from the subterranean formations. Measurements of the properties of the subterranean formations may be recorded with respect to a tool axial position (depth) within the wellbore as the tool is moved along the wellbore. Such recording is referred to as a well log.
Well logging tools (or tools in general) can be conveyed along the wellbore by extending and withdrawing an armored electrical cable (“wireline”), wherein the well logging tools are coupled to the end of the wireline. Extending and withdrawing the wireline may be performed using a winch or similar spooling device known in the art. However, such conveyance relies on gravity to move the well logging tools into the wellbore, which are used on substantially vertical wellbores. Wellbores deviating from vertical may require additional force for conveyance through the wellbore. For examples of conveyance techniques, see, e.g., U.S. Pat. No. 5,433,276, issued to Martain, et al., entitled “Method and System for Inserting Logging Tools into Highly Inclined or Horizontal Boreholes,” issued Jul. 18, 1995, and U.S. Pat. No. 6,092,416, issued to Halford, et al., entitled “Downhole System and Method for Determining Formation Properties,” issued Jul. 25, 2000, which are incorporated herein by reference in their entirety.
To operate and perform desired tasks such as measuring local environmental parameters and sampling formation fluids, several types of downhole valves are widely used with downhole tools to seal, for instance, a wired drill pipe string (or more commonly referred to as a wired drill pipe (“WDP”), which is a type of drill string including a communication channel (see, e.g., U.S. Pat. No. 6,641,434, issued to Boyle, et al., entitled “Wired Pipe Joint with Current-loop Inductive Couplers,” issued Nov. 4, 2003, which is incorporated herein by reference in its entirety). Most of these downhole valves are actuated electrically or hydraulically to switch between an open and a closed position, and these actuation tasks can initiate a sequence of sampling or measurement operations, processes, or very basic logic operations. The valves usually do not interact with an operator on the surface or the tool itself due to limited bandwidth of the communication channel coupled between the valve and surface computer system.
The harsh environment and very limited space within a downhole has not allowed introduction of more complex valves with feedback loops or extra electronics. To make things more difficult, the downhole valves by themselves can be unreliable, and can be the cause of day-to-day operational problems due to the limitations of space and the harsh working environment.
These limitations have now become substantial hindrances to safe and efficient drilling and measuring processes associated with forming and operating an oil or gas well. Thus, despite numerous product developments, no satisfactory strategy has emerged to overcome these limitations.